technology: Return error if no devices can be found for a technology

Instead of returning 0 (Success) when there are no devices for a given
technology, return ENXIO so that caller can inform user about the
issue.

src/technology.c

@@ -700,7 +700,7 @@ static int technology_affect_devices(struct connman_technology *technology,
 						connman_bool_t enable_device)
 {
 	GSList *list;
-	int err = 0;
+	int err = -ENXIO;
 
 	for (list = technology->device_list; list; list = list->next) {
 		struct connman_device *device = list->data;